1. Field of the Invention
The present invention relates to a suction roll for conveying in one direction a strip of flexible material such as a strip of paper, a resin film or a strip of sheet metal.
2. Description of Related Art
Conventionally, a suction roll for conveying a strip of flexible material has many pores on its circumference, and the pores are connected with a vacuum suction device such as a blower. While the air pressures in the pores are negative, the circumference of the suction roll holds the strip of flexible material.
Practically, only about a half of the circumference of the suction roll is in contact with the strip of flexible material, and the other half does not contribute to the suction of the strip. The pores on the latter half of the circumference are open to the outside, and the vacuum suction device takes in air through these pores. This lowers the efficiency of the vacuum suction device, thereby requiring a large-sized apparatus.
It is a conventional way of solving this problem that the half of the circumference of the suction roll which is out of contact with the strip is covered with a resin seal. In this way, however, the following problems occur: (1) even if a material which has a high abrasion resistance is used for the seal, the seal is abraded easily because of its function and must be exchanged frequently; (2) because dust is caused by the abrasion of the seal, the suction roller is not suitable for use in a clean room; (3) because the seal covers a large part (about the half) of the suction roll, a large power is required to rotate the suction roll; (4) processing of the surface of the seal which will be in contact with the suction roll and regulation of the pressure of the seal on the suction roll are difficult; and (5) because the seal cannot seal the pores perfectly, it is impossible to completely prevent the vacuum suction device from taking in air through the pores.